VIENNA — (CNN)  Hundreds of thousands of migrants are pounding on Europe’s invisible doors — dirty, exhausted and desperate to escape the daily carnage in their homelands.

But their arrival also puts a strain on European countries’ resources. Germany expects to take in 800,000 refugees and says it will spend at least 6 billion euros ($6.7 billion). Austria, which received 16,000 migrants in just two days, said it won’t be able to keep up with this pace.

At the same time, several oil-rich Arab nations closer to the conflict zones have come under harsh criticism because they’ve taken in virtually no refugees.

So, are countries obligated to house refugees? If so why?

For the most part, it boils down to an international treaty.

The 1951 Refugee Convention was adopted after World War II, when hundreds of thousands of refugees were displaced across Europe.

The treaty defined what a refugee is — someone who is seeking refuge from persecution. It also gives them a very important right — the right to not be sent back home into harm’s way, except under extreme circumstances.

“Since, by definition, refugees are not protected by their own governments, the international community steps in to ensure they are safe and protected,” said UNHCR, the United Nations’ refugee agency. The treaty was amended in 1967, in part to include refugees from around the world.

And according to the provisions, “refugees deserve, as a minimum, the same standards of treatment enjoyed by other foreign nationals in a given country and, in many cases, the same treatment as nationals,” the UNHCR said.

Over the decades, more than 50 million refugees have been resettled.

One hundred and forty two states have signed on to both the 1951 Refugee Convention and the 1967 protocol. Some signed on decades ago, and some joined just a few years ago.

Hungary is one of the signatories. But it has been criticized by migrants and activists who say refugees are left in decrepit conditions as they await transfer. Now, Hungary is erecting a fence at the Serbian border to help control the flow of migrants.

Countries outside of Europe are also stepping up. Venezuela, another signatory to the treaty, said it will take in 20,000 refugees. Australia said it has absorbed 4,500 refugees from Syria and Iraq over the past year.

Noticeably absent from the list: the Gulf states of Saudi Arabia, Kuwait, Bahrain, Qatar, Oman and the United Arab Emirates.

Well over 366,000 refugees have crossed the Mediterranean Sea to Europe this year, the UNHCR said. Another 2,800 attempted the journey, but either died or disappeared.

The vast majority of refugees come from three countries: Iraq, where migrants are fleeing the brutality of ISIS; Afghanistan, which has been devastated by war; and Syria, where civilians are grappling with both ISIS and indiscriminate attacks wrought by the country’s civil war.

In addition to not getting sent back to their home countries, refugees have several other rights, including:

– The right to not be punished for illegally entering countries that signed on to the treaty

– The right to housing

– The right to work

– Access to education

– Access to public assistance

– Access to courts

– The right to get identity and travel documents
Since those oil-rich Gulf states are close to Syria, Iraq and Afghanistan, it would seem natural that they’d help absorb some of the refugees, right?

Wrong.

Saudi Arabia, Kuwait, Bahrain, Qatar, Oman and the United Arab Emirates have each given millions of dollars to the United Nations to help Syrian refugees. But they haven’t housed any of them, according to Amnesty International.

“We’ve been asking not only (for) the borders of the region to be open, but all of the borders — especially in the developed world — also open,” said Antonio Guterres, U.N. High Commissioner for Refugees.

Abdul Khaleq Abdulla, a retired professor from United Arab Emirates University, said Gulf nations treat it as a matter of security.

“Having refugees also feeds into ISIS’ appeal,” Abdulla said. “And it feeds into the violence in the region, which is already the most violent region on Earth. So all in all, anything that goes in the neighborhood impacts the security and security of the Arab Gulf states who are by far the most stable and the most secure.”

And those Gulf states aren’t party to the international treaty — so technically, they don’t have to help.

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